Mitochondrial Excision-Amplification Plasmids in Senescent and Long-Lived Cultures of Podospora Anserina

Abstract

Senescence in the filamentous fungus Podospora anserina is maternally inherited. Several laboratories, including our own, have shown that specific regions of the mitochondrial genome excise and replicate as autonomous plasmids during senescence. One particular plasmid, termed α senDNA, is found most often, but others (β, e, and θ senDNAs) are also observed. DNA sequence analysis has shown that the 2.6-kbp α senDNA is a complete group II intron of the cytochrome oxidase subunit I (COI) gene. Like other group II introns, α senDNA codes for amino acid sequences that have considerable homology with retroviral reverse transcriptase. Beta senDNA is a 9.8-kbp element, and, of the 5 kbp sequenced thus far, no introns have been noted. Epsilon senDNA is 5.5 kbp, and, while it contains no group II introns, three group I introns were detected.